docs: POC #2 ran and passed — OQ-ST-03 closed (per-engine drivers: tokio-postgres+deadpool for pg), OQ-ST-04 ground complete

Findings: unified surface holds on tokio-postgres with the transactional
property intact (in-tx NOTIFY is commit-atomic; rollback drops all);
LISTEN wake beats poll 5-16x at p50 with 300/300 isolated delivery;
pooled-LISTEN discard (deadpool#360) verified and pinned as our own test;
postgres-notify 0.3.8 evaluated and passed over (lazy reconnect, no
initial-connect script, unquoted identifier LISTENs) in favor of the
~90-line hand-rolled forwarder with test-pinned pitfalls. sqlx PgListener
fallback retired unfired.

docs/research/poc-pg-posture-spec.md

@@ -1,5 +1,5 @@
 ---
-status: spec
+status: findings-filed
 title: "POC #2 — Postgres engine posture: LISTEN/NOTIFY wiring, the pool tx-seam, and reactive parity on tokio-postgres"
 last_updated: 2026-10-04
 ---
@@ -20,6 +20,15 @@ last_updated: 2026-10-04
 > `postgres-notify` 0.3.8 candidate (verified: reconnection + multi-
 > channel subscribe) — both folded in below; neither's *behavioral*
 > claims are trusted until probed.
+>
+> **Ran 2026-10-04: PASS** — findings in
+> [poc-pg-posture-findings.md](poc-pg-posture-findings.md). Both
+> pre-spec research claims verified in-probe and pinned as tests
+> (#360: pooled LISTEN registers but never delivers; postgres-notify:
+> reconnect + re-LISTEN verified *with* recorded quirks — lazy
+> reconnect, no script at initial connect, unquoted identifiers).
+> The spec's decision gate passed on all three conditions; OQ-ST-03
+> closed; the sqlx PgListener fallback retired unfired.
 
 ## What this POC must decide